The invention relates to determining and indicating the quantity of a stored liquid or solid product contained in a closed container of constant volume together with a gaseous or vaporous filling material filling the residual volume of the container interior and held under a limitedly variable pressure (overpressure or underpressure), varying from atmospheric pressure.
It is known to provide a gauge stick, float, pneumatic weighing appliance, etc. for determining the filling level of a liquid in a container and in this way to determine the quantity of the liquid. However, such methods and devices based on determining the filling level are dependent on the shape and position of the container, and the resulting measuring accuracy is limited. Frequently, both fixed and movable containers have a complicated three-dimensional shape, e.g. formed by pipe systems. In addition, during the journey or flight, the fuel containers of land, air and ocean craft are subject to regular position changes, and the liquid contained therein is also exposed to mass acceleration influences. It is therefore extremely important to have an accurate indication of the available liquid supply, which is independent of the shape and position of such containers, as well as of the effects of mass acceleration. However, high accuracy of measurement, independence from fault-prone mechanical filling level measuring devices, and the container shape are also important for stationary storage vessels, which do not change their position.
It is also known to determine the quantity of a stored liquid material on the basis of a flow measurement.